A steering apparatus such as illustrated in FIG. 18 has been widely used in order to apply a steering angle to the steered wheels (normally the front wheels) of an automobile. In this steering apparatus, a steering shaft 3 is supported so as to be able to rotate on the inner-diameter side of a cylindrical steering column 2 that is supported by the vehicle body 1. A steering wheel 4 is fastened to the rear-end portion of the steering shaft 3 that protrudes further toward the rear than the rear-end opening of the steering column 2. The rotation of the steering wheel 4 is transmitted to an input shaft 8 of a steering gear unit 7 by way of a universal joint 5a, an intermediate shaft 6 and a universal joint 5b. The rotation of the input shaft 8 pushes or pulls a pair of tie rods 9 that are located on both sides of the steering gear unit 7, which applies a steering angle to the steered wheels that corresponds to the amount that the steering wheel 4 was operated.
The steering apparatus may comprise a telescopic mechanism for adjusting the forward/backward position of the steering wheel 4 according to the size and driving posture of the operator. In the telescopic mechanism, the steering column 2 is constructed such that the rear-end section of a front-side inner column 10 fits inside the front-end section of an outer column 11 so that relative displacement in the axial direction is possible, and such that the entire length is able to extend or contract in a telescopic shape, and the steering shaft 3 is constructed such that an outer tube 12 is combined with an inner shaft 13 with a spline joint or the like so that torque can be transmitted and so as to be able to freely extend and contract. In the example in FIG. 18, a tilt mechanism is also assembled in order to adjust the up/down position of the steering wheel 4. Furthermore, an electric-powered power steering apparatus having an electric motor 14 as an auxiliary power source is also assembled, and this electric-powered power steering apparatus makes it possible to reduce the force required for operating the steering wheel 4. More specifically, a housing 15 that houses a worm reduction gear or the like is connected and fastened to the front-end section of the steering column 2, and this housing 15 is supported by the vehicle body 1 so as to be able to pivotally displace around a horizontal shaft 16. Moreover, a column-side bracket 18 that is fastened to part of the steering column 2 is supported by a support bracket 17, which is supported by a different location of the vehicle body 1, and is supported so as to be able to displace in the forward/backward direction and up/down direction.
Except for electric powered devices, in the tilt mechanism and telescopic mechanism, it is necessary, based on the operation of an adjustment lever, to be able to switch between a state in which the position of the steering wheel 4 can be adjusted, and a state in which the adjusted position can be maintained. Therefore, as illustrated in FIG. 19, a slit 19 that extends in the axial direction is provided on the bottom surface of a portion near the front-end section and middle of the outer column 11, and this slit 19 makes it possible for the inner diameter of the front-end section of the outer column 11 to expand or contract. A pair of held plate sections 20 is provided in portions on both sides in the width direction of the slit 19. Long holes 21 in the forward/backward direction that extend in the axial direction of the outer column 11 are formed in portions of the pair of held plate sections 20 that are aligned with each other. Moreover, long holes 23 in the up/down direction that are partially arc shaped centered around the horizontal shaft 16 are formed in a pair of support plate sections 21 that are parallel with each other and that hold the held plate sections 20 on both sides in the width direction. An adjustment rod 24 is inserted through the long holes 21 in the forward/backward direction and the long holes 23 in the up down direction. A head section 25 that is provided on the base-end section of the adjustment rod 24 engages with the long hole 23 in the up/down direction that is formed in one (right side in FIG. 19) of the support plate sections 22 so that displacement is only possible along the long holes 23 in the up/down direction, or in other words, in a state so that rotation is prevented. On the other hand, a cam apparatus 29 that comprises a drive-side cam 27 and a driven-side cam 28 is provided between a nut 26 that is screwed onto the tip-end section of the adjustment rod 24 and the outside surface of the other (left side in FIG. 19) support plate section 22. The drive-side cam 27 is rotated and driven by an adjustment lever 30. By providing a thrust bearing 53 between the outside surface of the adjustment lever 30 and the nut 26, the operational feeling when operating the adjustment lever 30 is improved.
When adjusting the position of the steering wheel 4, the adjustment lever 30 is rotated in a specified direction, which rotates and drives the drive-side cam 27 and reduces the dimension in the axial direction of the cam apparatus 29. As a result, the space between the inside surfaces that face each other of the driven-side cam 28 and the head section 25 is increased, and the force that the support plate sections 22 apply to the held place sections 20 is released. As the same time, the inner diameter of the portion of the front section of the outer column 11 where the rear section of the inner column 10 fits is elastically expanded, and the pressure acting on the area of contact between the inner-circumferential surface of the front section of the outer column 11 and the outer-circumferential surface of the rear section of the inner column 10 decreases. In this state, adjustment of the up/down position and the forward/backward position of the steering wheel 4 is possible within the range that the adjustment rod 24 is able to displace inside the long holes 21 in the forward/backward direction and the long holes 23 in the up/down direction.
After the steering wheel 4 has been moved to a desired position, the adjustment lever 30 is rotated in a direction opposite the specified direction, which increases the dimension in the axial direction of the cam apparatus 29. As a result, the space between the inside surfaces that face each other of the driven-side cam 28 and the head section 25 is reduced, and the held plate sections 20 are firmly pressed by the support plate sections 22. At the same time, the inner diameter of the portion on the front section of the outer column 11 where the rear section of the inner column 10 fits is elastically reduced, and the surface pressure that acts on the area of contact between the inner-circumferential surface of the front section of the outer column 11 and the outer-circumferential surface of the rear section of the inner column 10 increases. As a result, the up/down position and forward/backward position of the steering wheel is maintained in the adjusted position.
In recent years, as a countermeasure against automobile theft, various kinds of anti-theft apparatuses have been provided in automobiles. One kind of such an apparatus that is widely used is a steering lock apparatus that makes operation of the steering wheel impossible unless a proper key is used. FIG. 20 illustrates an example of a steering lock apparatus as disclosed in JP 2008-265646 (A). The steering lock apparatus 32 has a lock unit 33 that is provided on part of the steering column 2a and a key-lock collar 35 that is fitted around and fastened to the outside of part of the steering shaft 3a in a position that coincides with the phase in the axial direction of the lock unit 33 and is provided with an engaging concave section 34 that is formed in at least one location in the circumferential direction of this key-lock collar 35. During operation (when the key is locked), the tip-end section of a lock pin 36 of the lock unit 33 is displaced toward the inner-diameter side of the steering column 2a through a lock hole 37 that is formed in the middle section in the axial direction of the steering column 2a, and by engaging with the engaging concave section 34, rotation of the steering shaft 3a becomes practically impossible. In other words, when an attempt is made to rotate the steering wheel 4 with a force that exceeds a specified value (value regulated by key lock regulation) when the ignition is OFF and the engaging concave section 34 and lock pin 36 are engaged, the steering shaft 3a rotates with respect to the key-lock collar 35. However, the steering shaft 3a does not rotate when an attempt is made to rotate the steering wheel 4 with a normal operating force.
When assembling the steering lock apparatus 32 in the steering apparatus, the lock unit 33 is provided on the outer-diameter side of the steering column 2a, and the key-lock collar 35 is provided on the inner-diameter side of the steering column 2a. Therefore, in order to place the key-lock collar 35 on the inner-diameter side of the steering column 2a so as to be able to rotate, and to make it possible for the lock pin 36 and key-lock collar 35 to become completely disengaged without increasing the stroke of the lock pin 36, it is necessary to make at least the outer diameter of the portion of the steering column 2a where the steering lock apparatus 32 is assembled small and the inner diameter of this portion large, or in other words, it is necessary to make the thickness of the steering column 2a thin in that portion.
FIG. 21 illustrates an outer column 11a that is disclosed in JP 2007-223383 (A). An outer column 11a is integrally formed by casting using a light alloy such as an aluminum alloy, magnesium alloy or the like. A fitting support portion 31 for the end section of a cylindrical shaped inner column 10 (see FIG. 18) to fit into so that relative displacement is possible in the axial direction is provided on the end section in the axial direction of the outer column 11a, and a lock hole 37a for assembling the steering lock apparatus 32 is provided in the middle section in the axial direction of the outer column 11a. In an outer column 11a having this kind of construction, there is a possibility that the strength required when the steering lock apparatus 32 is operated will not be sufficiently maintained. In other words, when an attempt is made to rotate the steering wheel 4 with a large force when the lock pin 36 that protrudes toward the inner-diameter side of the outer column 11a through the lock hole 37a is engaged with the engaging concave section 34 of the key-lock collar 35, there is a possibility that the lock hole 37a will deform due to an excessively large force. Therefore, in order to prevent this kind of deformation, it is necessary to sufficiently maintain the strength of the outer column 11a. In order for that, increasing the wall thickness of the outer column 11a, or making the outer column 11a using an iron-based material is possible, however, in that case, a problem occurs in that the overall weight of the steering column increases.